Prior known systems for exhausting food fumes and smoke from cooking apparatus, such as food fryers, required the exhaust to be vented out of the building since it was not formerly possible to cleanse grease-laden air sufficiently for recirculation. Stamps, U.S. Pat. No. 4,489,647, describes a ventless exhaust system only for use with an enclosed, small-scale, unpressurized, food frying and dispensing apparatus for cooking individual portions of food for which a short cooking cycle is sufficient and only a small quantity of exhaust gas is produced.
The patent to Glover, U.S. Pat. No. 3,747,301, describes a smoke eliminator for use above burners or grills, but does not address the problem of cleaning exhaust from large scale fryers sufficiently for recirculation. Gaylord, U.S. Pat. No. 3,785,124, includes a grease extractor hood section and a deodorizing section in order to purify air being vented to the outside atmosphere. King, U.S. Pat. No. 3,907,525 describes a similar system for cleaning air before exhausting it to the atmosphere. The patent to Ebert, U.S. Pat. No. 3,744,217, describes a high-voltage ozone-free electrostatic air filter suitable for use over a kitchen oven.
Other patents, such as those to Kuechler, U.S. Pat. No. 4,952,640 and 4,085,736 and 4,250,870, describe a vortex system for exhausting air.